BOBIGNY, France—Three days before the attacks that ripped through Paris, Djazira Boulanger handed the keys to her row house, across the street from a kindergarten, to a guest who had booked it over the website Homelidays.com. His name was Brahim Abdeslam.

She didn’t know that Mr. Abdeslam was a central figure in plotting the deadly assault. As Ms. Boulanger tended to her two young children at home, authorities say Mr. Abdeslam and a band of cohorts were down the street preparing weapons for an assault on the Stade de France...